Potential impact: Accidental and operational
oil spills in ports and harbours can cause
disturbance, damage and/or death to marine
habitats and species, including marine mammals,
birds, benthic communities, fish and saltmarsh.
Oil can cause the following impacts on marine
wildlife and habitats:

physical disturbance due to smothering
and direct toxic effects,

organic enrichment possibly causing localised
removal of oxygen,

contamination of sediments can lead to
the storage of persistent toxic oil constituents,
such as heavy metals.

Clean up activities may also cause impacts
on wildlife:

Dispersants prevent and minimise the spread
of oil, but also promote its penetration
into the sediments, potentially affecting
fish and other sensitive intertidal communities.

Physical damage caused to benthic plants
and animals during clean up operations.

Although relatively rare, major accidental
oil spills do happen and can potentially cause
a major impact on marine SACs. However, the
majority of oil spills reported in ports and
harbours are small and result from operational
activities. The potential impacts from oil
spills depend upon the type and quantity of
oil, location of spill, hydrodynamic conditions,
proximity to sensitive marine habitats and
species, and, where appropriate, the effect
of emergency response. In industrialised estuaries
and bays it is difficult to distinguish between
the effects of the numerous sources, and research
is needed. Oil pollution prevention is cheaper
in the long-term, than attempts to clear up.

Oil spill contingency planning according
to regulations and guidelines and effective
response to avoid and minimise effects.

Identify areas where the use of dispersants
presents little or no concern, and areas containing
sensitive marine features where their use
should be avoided, unless there is greater
risk of oil pollution damage on marine features.

It is difficult, although possible, to distinguish
the effects due to ship’s litter and other
sources of marine litter. Impacts depend on
amounts and types of litter. Problems are
mostly associated with persistent plastics.
Entanglement and ingestion of plastic litter
by birds and mammals occurs in UK waters,
but the incidence rate is unknown.

Potential impact: Discharges of high
concentrations of sewage may cause a localised
deterioration in water quality, which may
result in oxygen depletion, increased suspended
solids, nutrient enrichment and increased
risk of algal blooms which may disturb animals
and plants. Chemical additives in portable
toilets and holding tanks (including chlorine,
ammonium & zinc) are toxic to marine life.
Generally the impacts associated with sewage
discharged by recreational craft are minimal
in comparison with those which arise from
the far greater amounts discharged from land-based
sources. Impacts are generally localised and
temporary.

Potential impacts depend on numbers of vessels,
amounts of sewage, water quality, temperature
and depth, tidal movement and proximity of
sensitive species. Greatest effects are likely
to occur when many vessels congregate in enclosed
areas or shallow water with little or no tidal
exchange in summer and autumn. In some cases
nutrient enrichment from sewage may increase
productivity, the benefits of which are likely
to be seen in higher organisms in estuaries
or bays, such as feeding bird populations.
However, despite small possible incidental
benefits, this should not be to the detriment
of water quality in the site.

Encourage use of shore-side toilet facilities,
holding tanks where fitted and disposal of
waste at pump-out facilities, and while underway
as far offshore as possible in areas where
strong currents ensure dispersion and dilution.

Discourage/prohibit discharge of sewage wastes
where doing so would harm marine features.

Issue: Discharge of ballast water

Key process: Introduction of non-native

species

Potential impact: The introduction
of non-native animals and plants in ships
ballast water may have a range of effects,
from undetectable to the complete detriment
of native communities. Species introduced
to the UK from ballast water include various
bloom forming phytoplankton, a number of fouling
organisms, marine benthic animals that compete
with native communities and an American cordgrass
Spartina species, which crossed with
the native species to form common cordgrass
that has since spread throughout Britain,
replacing native saltmarsh species.

In the UK, around 80% of introduced species
have no effect, however 20% from a number
of sources do have some effect on native communities,
in many cases causing disturbance and damage.
The introduction and potential effects of
harmful non-native species are highly unpredictable,
but can be very serious.

Min/Adv

Comply with IMO guidance and support MCA
in encouraging shipowners to comply with IMO
guidance.

Inform local agents and ships of areas where
uptake of ballast water should be avoided.

Encourage the exchange of ballast water at
sea, where it is considered safe to do so,
which will be regulated by the MCA

Discourage / prohibit the unnecessary discharge
of ballast water in the port and harbour area,
where appropriate.